Department of Biopharmaceutics, Graduate School of Pharmaceutical Sciences, Nagoya City University, Mizuho-ku, Nagoya, Japan.
Department of Biopharmaceutics, Graduate School of Pharmaceutical Sciences, Nagoya City University, Mizuho-ku, Nagoya, Japan.
J Biol Chem. 2022 Aug;298(8):102161. doi: 10.1016/j.jbc.2022.102161. Epub 2022 Jun 17.
Recent studies have shown that human solute carrier SLC19A3 (hSLC19A3) can transport pyridoxine (vitamin B6) in addition to thiamine (vitamin B1), its originally identified substrate, whereas rat and mouse orthologs of hSLC19A3 can transport thiamine but not pyridoxine. This finding implies that some amino acid residues required for pyridoxine transport, but not for thiamine transport, are specific to hSLC19A3. Here, we sought to identify these residues to help clarify the unique operational mechanism of SLC19A3 through analyses comparing hSLC19A3 and mouse Slc19a3 (mSlc19a3). For our analyses, hSLC19A3 mutants were prepared by replacing selected amino acid residues with their counterparts in mSlc19a3, and mSlc19a3 mutants were prepared by substituting selected residues with their hSLC19A3 counterparts. We assessed pyridoxine and thiamine transport by these mutants in transiently transfected human embryonic kidney 293 cells. Our analyses indicated that the hSLC19A3-specific amino acid residues of Gln, Gly, Ile, Thr, Trp, Ser, and Asn are critical for pyridoxine transport. These seven amino acid residues were found to be mostly conserved in the SLC19A3 orthologs that can transport pyridoxine but not in orthologs that are unable to transport pyridoxine. In addition, these residues were also found to be conserved in several SLC19A2 orthologs, including rat, mouse, and human orthologs, which were all found to effectively transport both pyridoxine and thiamine, exhibiting no species-dependent differences. Together, these findings provide a molecular basis for the unique functional characteristics of SLC19A3 and also of SLC19A2.
最近的研究表明，人类溶质载体 SLC19A3（hSLC19A3）除了其最初鉴定的底物硫胺素（维生素 B1）外，还可以转运吡哆醇（维生素 B6），而大鼠和小鼠的 hSLC19A3 同源物可以转运硫胺素但不能转运吡哆醇。这一发现表明，一些对吡哆醇转运至关重要但对硫胺素转运不重要的氨基酸残基是 hSLC19A3 所特有的。在这里，我们试图通过比较 hSLC19A3 和小鼠 Slc19a3（mSlc19a3）来鉴定这些残基，以帮助阐明 SLC19A3 的独特作用机制。为此，我们通过用 mSlc19a3 中的相应氨基酸残基替换选定的氨基酸残基来制备 hSLC19A3 突变体，并用 hSLC19A3 中的相应氨基酸残基替换选定的氨基酸残基来制备 mSlc19a3 突变体。我们通过瞬时转染的人胚肾 293 细胞评估了这些突变体对吡哆醇和硫胺素的转运。我们的分析表明，hSLC19A3 特有的 Gln、Gly、Ile、Thr、Trp、Ser 和 Asn 等氨基酸残基对吡哆醇的转运至关重要。这些 7 个氨基酸残基在能够转运吡哆醇但不能转运吡哆醇的 SLC19A3 同源物中大部分是保守的，但在不能转运吡哆醇的同源物中则不然。此外，这些残基在包括大鼠、小鼠和人在内的几个 SLC19A2 同源物中也被发现是保守的，它们都能有效地转运吡哆醇和硫胺素，没有种属依赖性差异。总之，这些发现为 SLC19A3 和 SLC19A2 的独特功能特性提供了分子基础。
